Research On The Optimization Of Supplementary Cementitious Activity Of Steel-making Slag From Anyang Steel And Iron Group

In China, resource utilization of industrial waste is one of the most important measures for the sustainable development of industry, and the absorption of industrial waste in cement and concrete industry has become one of effective paths for the implementation of circular economy for industry. Steel-making slag (SS) is one of main industrial wastes discharged in the process of steel-refining by steel enterprises, and it could be utilized resourcefully in cement and concrete, which is one of the effective ways of high additional value utilization of SS and has very important significance not only for iron and steel industry but also for cement and concrete industry.In order to provide some effective experiment and theoretical basis for the resource utilization of SS from Anyang iron and steel group, the present research work was concentrated on the utilization of steel slag as active supplementary cementitious admixtures in cement and concrete. Research about the feasibility of utilization of some other industrial wastes (i.e. phosphogypsum, desulfurization gypsum and spontaneous combustion gangue) in the cement containing SS was also carried out. Several conclusions could be obtained according to these research results.(1) When some SSs after appropriate treatment were added to cement as active admixture, cement needed less water for standard consistency and did not exhibit any bad problems in soundness. Results showed that, cement (grade 42.5) could be obtained by replacing less than 30% of clinker with SSs. Even when the addition proportion of SS increased to 40%, cement (grade 32.5) could also be obtained, and performance of all cements containing SSs could meet the requirement of China national standard of GB 175-2007.(2) The particle size distribution of SS was the most important factor for depending its activity. Steel slag particles of different sizes had different mineral compositions, which might be the basic reason for the great difference in their activities. In SS sources, fine SS particles (<5 mm) could be ground very easily in a ball mill. Coarse SS particles (>5 mm) had bad grindability, but they showed excellent later activity and so should be also utilized effectively.(3) Grey correlation analysis results showed that, in all SS particles, the mass fractions of<30.2μm and>30.2μm particles had a positive and negative effect on the strength of relevant cement, respectively. The mass fraction of 10.0～19.9μm particles had a maximum effect on the strength of cement at all ages, and the fractions of>45.7μm and<5.0μm SS particles had just a minor effect on the cement strength. In order to obtain SS with optimum particle size distribution, which could lead to high activity, it was necessary to increase the mass fraction of 10.0～30.2μm SS particles, limit the mass fraction of<5.0μm SS particles and decrease that of>30.2μm SS particles.(4) When SS were added into cement with other admixtures, three composite cements (i.e. SSCG7, SSCG8, SSFAS7) could be obtained after some optimization work based on the properties and production cost of cement. Besides for excellent performance and low grinding cost, some waste gypsums (i.e. phosphogypsum or desulfurization gypsum) were also used in these cements.(5) According to durability experiment results, cements containing SS exhibited better sulfate resistance and excellent growth rate of later strength, compared with Portland cement. However, cements containing SS displayed poor volume stability and frost resistance, which were mainly determined by the fineness of SS and could be improved to some degree by combining with admixture (coal gangue and fly ash).(6) When SS powder were individually added to concrete as additive, the workability of concrete could be improved, and the optimized replacement ratios of cement was 10%～20%. And the combined admixture with SS and coal gangue could substitute about 20% of cement without deterioration in performance of concrete. And the above three composite cements could be directly used in the preparation of concrete and exhibited excellent performance.